As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature processed) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
The packaging material has a multilayer structure comprising a layer of fibrous material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of oxygen-barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product.
A typical example of such a package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is formed from a continuous tube obtained by bending and longitudinally sealing a web packaging material; the web of packaging material is sterilized on the packaging machine itself, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, after sterilization, is removed, e.g. vaporized by heating, from the surfaces of 10 the packaging material; and the web of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and cut at equally spaced cross sections to form pillow packs, which are then folded mechanically to form the finished, e.g. substantially parallelepiped-shaped, packages.
Two basic types of web-fed filling and forming machines are known: a first and more common type is a machine having two pairs of reciprocating jaws; this type of machines includes, e.g the TB and TBA series produced by Tetra Brick Packaging Systems at LUND (Sweden), Ruben Rausings gata and at Modena (Italy), Via Delfini 1. The second type of web-fed packaging machine is the endless chain type, wherein forming and sealing units are carried by two facing endless chains rather then by reciprocating jaws.
To allow folding of the web packaging material both during forming and final folding., crease lines defining a so-called “crease pattern” are formed on the packaging material at the production line.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming mandrel, and the resulting packages are filled with the food product and sealed. One example of such a package is the so-called “gable-top” package commonly known by the trade name Tetra Rex (registered trademark), which has a gabled top portion defined by two inclined or sloping walls joined together at a top transversal seal.
In particular, once formed on the forming mandrels, the unfinished packages have an upwardly opened parallelepiped shape; the gabled top portion is obtained by compressing opposite side walls of the upper portion of the unfinished packages towards each other in order to draw up the upper edges of the other walls, which are then sealed together to form the transversal seal.
Once formed, packages of the above type may undergo further processing steps, such as the application of a re-closable opening device.
Gable-top packages are very conveniently used in combination with re-closable opening devices because the sloping top walls are wider than corresponding flat portions of parallelepiped and therefore allow the application of larger opening devices, e.g. provided with screw caps or the like.